How Apache Cassandra® Balances Consistency, Availability, and Performance

The CAP theorem states that a distributed database cannot guarantee consistency, availability, and partition tolerance simultaneously. In practice, databases tend to be either CP (prioritizing consistency over availability) or AP (prioritizing availability over consistency). Apache Cassandra is usually described as an AP system, ensuring data availability at the expense of consistency. It maintains tunable consistency levels for read and write operations, allowing users to specify the number of replicas that need to respond for a successful operation. A higher consistency level ensures accuracy but impacts latency. Developers can configure these behaviors individually for each operation, managing trade-offs between consistency, availability, and performance.